Gas turbine engines mix compressed air with fuel for ignition in a combustor to generate combustion gases from which energy and power are generated. The typical air pollutants produced by gas turbines burning conventional hydrocarbon fuels are nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons. It is known in the art that the rate of NOx formation is exponentially dependent on temperature, which, in turn, correlates to the fuel-air ratio of the mixture fed into the combustion chamber. To reduce the pollutant emissions, fuel and air are premixed to a lean mixture prior to combustion.
Recently, gas turbines are starting to use coal-derived synthesis gas (“syngas”) as a means to convert coal into power with lower pollutant emissions than traditional coal plants. Some syngas fuels, such as ones containing large amounts of hydrogen, are highly reactive so that flame holding, autoignition, and flashback problems are more likely to occur in the premixer, consequently degrading emissions performance and causing hardware damage due to overheating.
It is known in the prior art that recirculation zones may occur in the premixer. For example, fuel injection into a crossflow of air often creates recirculation zones behind the fuel jets where the fuel participates in a secondary flow, causing the fuel to reside in this area much longer than outside of the area. For highly reactive fuels, high flame speeds and short blow-off times mean that flame holding is more likely to occur in the low-speed recirculation zones. Some premixers can reduce the tendency for flame holding for highly reactive fuels, but often at the expense of incurring large pressure drops in the premixer. Thus, there exists a need for an air/fuel premixer that can be used with highly reactive fuels without compromising turbine efficiency, functionality, or life cycle.
Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. Unless otherwise defined, all technical and scientific terms and abbreviations used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and compositions similar or equivalent to those described herein can be used in the practice of the present invention, suitable methods and compositions are described without intending that any such methods and compositions limit the invention herein.